- This cleans up a lot of stuff. The actual substance is addition of
account_current_callstack in handle_event.c (which however uses
those cleaned-up interfaces).
- trace-exec.exp was extended to check that the exec syscall can be
seen in -c output. That's one of the symptoms of what this fixes.
- This hides dict_opt_c in summary.c. It also gets rid of the global
variable current_time_spent--instead, the information is passed via
a function argument in a struct timedelta (so that we never confuse
absolute time with relative). callstack_element.time_spent was renamed
to .enter_time, as that is what it has always been.

- "string" lens and "format" pack were extended such that using an
integer as underlying array type denotes a wide character string.
- several prototypes from wchar.h were added to libc.so.conf.
- ltrace.conf.5 was updated

- That means we have to copy them out of ELF ahead of time instead of
referencing them from inside ELF on demand. But this way we can keep
one grand vector of all PLT-like relocations. On PPC, this makes
a difference: some PLT-like relocations (R_PPC64_JMP_IREL in
particular) are stored in .rela.dyn, not .rela.plt.

- The function destroy_global_config was called from normal_exit even
if init_global_config hadn't been called before, such as when ltrace
was run with no command line arguments. This led to crashes. We
avoided similar crashes due to exit from init_global_config by
calling _Exit instead.
- Instead, schedule execution of destroy_global_config only after it
is known that init_global_config was successful. Replace the clumsy
_Exit calls again by plain exit.

Also allow parsing colon-separated lists into opt_F. This will be useful
for -F as well as for parsing some environment variables.
This removes bits related to default directories to look into. This will
eventually be moved to os_get_config_dirs, currently it's simply disabled.
The code in libltrace.c is currently incompatible with opt_F being a vector,
so it's disabled as well. Revamp of the whole configury shebang underway.

This is for consistency with other structures, and ultimately with
Linux coding style. The typedef ("Process") was dropped as well for
this reason.
This opportunity was used to fix coding style around the impacted
lines.

- in callstack_pop, we don't free arch_ptr. That's because this doesn't
get copied over the clone. It's a mere coincidence that fork() doesn't
need to save register arguments, and this works.
- added copyright notices to files that this touches. This is based on
git blame. Only contributors of 10+ lines are added
- test suite adjusted to not include "void" type as "don't show this int".
Back ends in general need to know the exact type, so this never worked
anyway.